About thirty million people in the US undergo a liver disorder for different causes and about 27,000 deaths are registered annually in the US due to liver disease. At this time, the only definitive treatment of hepatic failure is orthotopic transplantation. However, there is a critical shortage of organs, with a deficit of ~3,000 livers per year. Similar numbers affect most organs & tissues, with the total organ waiting list currently at 100,000 requests and the number increasing by 5% every year. Given that only organs in pristine condition are transplantable, orthotopic transplantation will always remain a limited pool. A more elegant, long-term solution is using stem cells to develop tissue-engineered replacements. However, while many in vitro successes have been demonstrated, clinical success has been very limited due to low cell viability and functionality in the long term in vivo. The major gap is the lack of an ideal transplantable scaffold that has all the necessary microstructure and extracellular cues for cell attachment, differentiation, function and vascularization, which has so far proven difficult to manufacture in vitro. Our long-term goal is to engineer transplantable liver grafts for curing or treating liver dysfunction and failure. The objective of the proposed study is to develop functional and transplantable rat liver grafts. The central hypothesis to be tested here is that the natural liver scaffold derived from discarded livers can be extensively repopulated, can provide an adequate maturation environment for stem cell derived hepatocytes, and that these grafts perform the essential hepatic functions in vitro and in vivo. The rationale of the study is that while most research focuses on producing the ideal scaffold from the ground up using synthetic biomaterials, the native ECM is likely to contain the necessary architecture and environmental cues, hence presents a promising, little explored alternative approach for producing organ grafts which can vertically advance the field of tissue engineering. The research team assembled has expertise on perfusion systems, tissue engineering, stem cell engineering, and liver transplantation (see Biographical Sketches), which are necessary to perform the proposed studies. Engineering of functional liver grafts from stem-cell derived hepatocytes and liver's natural matrix is an innovative endeavor, as it has the potential to become a novel platform for hepatic tissue engineering. The work described here is expected to lead to a novel graft engineering approach to provide auxiliary hepatic support. While this work utilizes liver as the model organ, the results of this work will also have a positive impact by establishing the basis of future sophisticated organ engineering techniques that incorporate several different cell types and can be applied to other organs (pancreas, kidney, etc.), and may ultimately lead to development of entire organs in vitro. The ESC maturation protocol developed here is expected to be a significant contribution to the field of stem cell engineering. Hepatocyte culture in the decellularized matrix may also prove to be a new platform for pharmaceutical studies.